DUAL STRATEGIES OF SONG DEVELOPMENT IN AMERICAN REDSTARTS, SETOPHAGA-RUTICILLA

Like certain other paruline warblers, American redstarts, Setophaga ruticilla, divide their total repertoire of territorial songs into functional subsets. The repertoire consists of a single 'repeat' song and a 'serial' set comprising the remaining songs. To determine whether their repertoires changed with age, individuals were recorded in successive years on their breeding grounds in New Brunswick, Canada. Only three (5%) of 64 males changed their repeat songs from one year to the next (N = 88 annual returns), apparently modelling the new songs after those of neighbours. In contrast, redstarts frequently changed serial songs from year to year, based on results from 43 birds in 59 annual returns. All males that returned as 2-year-old adults either added or deleted serial songs, or did both. Also, over 40% of adults returning as 3- or 4-year-olds added new serial songs and/or deleted songs used in a previous breeding season. Evidence indicated that new songs were copied from neighbours. Retention or deletion of a serial song between the subadult and first adult year could be predicted on the basis of whether it was shared with a neighbour in either of the 2 years. Repertoire sizes remained essentially constant across ages. Differences in the developmental strategies of the two song modes and their functions were related to the expression of song neighbourhoods. © 1994 The Association for the Study of Animal Behaviour.